A patent document 1 discloses an art for an EGR (Exhaust Gas Recirculation) device of an engine for recirculating a part of exhaust gas into intake air, wherein accuracy of estimation of a flow rate of EGR gas is enhanced by calculation taking account of pulsation of the EGR gas. Specifically, for the EGR device, it is configured to: employ sensors to sense pressures at upstream and downstream sides of an EGR valve provided in an EGR passage; make a conversion into a sine wave from fluctuations in pressure ratio during a predetermined time period; calculate a pressure function, based on the sine wave, wherein the pressure function is used to calculate the flow rate of EGR gas from a pressure ratio as a variable; and calculate the flow rate of EGR gas flowing in the EGR passage during the predetermined time period, by using the pressure function.